How does disturbance shape Canada's forests?

Canada’s forests are continually affected by fire, insects and disease. These natural disturbances – and others including drought, floods and windstorms – can renew whole forest landscapes and, over time, shape forest composition, structure and habitat diversity.

Natural disturbances vary in severity, extent and frequency, and their relative importance varies from region to region. The result is that Canada’s forests are in a constant state of change and are part of a dynamic landscape.

Forest fire causes in Canada (2007-2017)
Graphic displaying forest fire causes in Canada between 2007 and 2017 by average number of fires, showing: (1) 44% lightning, (2) 41% human (excluding industry), (3) 8% unknown, (4) 7% industry. Graphic displaying forest fire causes in Canada between 2007 and 2017 by average area burned, showing; (1) 74% lightning, (2) 22% unknown, (3) human (excluding industry), (4) 1% industry.
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Graphic displaying forest fire causes in Canada between 2007 and 2017 by average number of fires, showing: (1) 44% lightning, (2) 41% human (excluding industry), (3) 8% unknown, (4) 7% industry.

Graphic displaying forest fire causes in Canada between 2007 and 2017 by average area burned, showing; (1) 74% lightning, (2) 22% unknown, (3) human (excluding industry), (4) 1% industry.

Natural disturbances bring renewal

Natural disturbances like fire, insect outbreaks and disease are an important component of the natural life cycle of forests, especially Canada’s boreal forests.

In the boreal zone, fire is the primary agent of change and renewal, not only releasing nutrients and allowing sunlight to reach the forest floor, but even releasing the seeds of some species from their cones.

Disturbance has positive and negative effects

Extensive stand mortality sometimes results from large insect outbreaks and diseases, releasing nutrients from affected trees and reducing competition among surviving and newly establishing trees. This in turn enhances forest renewal and succession. However, exotic or non-native insects and diseases introduced through global trade can have negative rather than positive impacts, since Canada’s native forests may not be adapted to them.

While natural disturbances are essential to forest health and renewal, they can have a negative impact on the people, communities and businesses that reside in or rely on forests. Fire poses threats to human safety, property and infrastructure, but natural disturbances can also temporarily reduce the supply of timber, with socio-economic impacts on communities and citizens.

Disturbances affect the carbon cycle

Since forests absorb carbon as they grow and release it when they die and decay or when they burn in forest fires, they play an important role in the carbon cycle. The impacts of natural disturbances, especially fire, are among the many complex factors that determine whether forests absorb or release more carbon each year.

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